This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A333696 #10 Apr 03 2020 12:06:26
%S A333696 1,2,3,4,5,2,7,8,9,10,11,12,13,14,5,16,17,6,19,20,3,22,23,24,25,26,27,
%T A333696 28,29,10,31,32,11,34,5,36,37,38,39,40,41,2,43,4,15,46,47,16,49,50,17,
%U A333696 52,53,18,55,56,57,58,59,20,61,62,63,64,65,22,67,68,23,10
%N A333696 Denominators of coefficients in expansion of Sum_{k>=1} phi(k) * log(1/(1 - x^k)).
%F A333696 a(n) = denominator of Sum_{d|n} phi(n/d) / d.
%F A333696 a(n) = denominator of Sum_{k=1..n} 1 / gcd(n,k).
%F A333696 a(n) = denominator of sigma_2(n^2) / (n * sigma_1(n^2)).
%e A333696 1, 3/2, 7/3, 11/4, 21/5, 7/2, 43/7, 43/8, 61/9, 63/10, 111/11, 77/12, 157/13, 129/14, 49/5, ...
%t A333696 nmax = 70; CoefficientList[Series[Sum[EulerPhi[k] Log[1/(1 - x^k)], {k, 1, nmax}], {x, 0, nmax}], x] // Denominator // Rest
%t A333696 Table[Sum[EulerPhi[n/d]/d, {d, Divisors[n]}], {n, 70}] // Denominator
%t A333696 Table[Sum[1/GCD[n, k], {k, n}], {n, 70}] // Denominator
%t A333696 Table[DivisorSigma[2, n^2]/(n DivisorSigma[1, n^2]), {n, 70}] // Denominator
%o A333696 (PARI) a(n) = denominator(sumdiv(n, d, eulerphi(n/d) / d)); \\ _Michel Marcus_, Apr 03 2020
%Y A333696 Cf. A000010, A000203, A001157, A018804, A057660, A070999, A071000 (fixed points), A071708, A072155, A074947, A074949, A333695 (numerators).
%K A333696 nonn,frac
%O A333696 1,2
%A A333696 _Ilya Gutkovskiy_, Apr 02 2020